We use a wall-hung water heater - is that what you mean? The Baxi Luna, I think it's called. It's really small and hangs . . . uh . . . on the wall, as you may have guessed.

Could be. The first one in my search was actually ceiling-hung, but maybe I'll find more options by searching for wall-hung units. You can see the ledge that runs around most of the perimeter. It would simply be handier to stuff the water heater up into that space than keep it taking up floor space. How do you like your wall-hung?